Groups of cells similar in structure and function Types of tissues

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1 Tissues Groups of cells similar in structure and function Types of tissues Epithelial tissue Connective tissue Muscle tissue Nerve tissue

2 Nervous tissue: Internal communication Brain, spinal cord, and nerves Muscle tissue: Contracts to cause movement Muscles attached to bones (skeletal) Muscles of heart (cardiac) Muscles of walls of hollow organs (smooth) Epithelial tissue: Forms boundaries between different environments, protects, secretes, absorbs, filters Skin surface (epidermis) Lining of GI tract organs and other hollow organs Connective tissue: Supports, protects, binds other tissues together Bones Tendons Fat and other soft padding tissue Figure 4.1

3 Epithelial Tissue (Epithelium) Sheet of cells that covers a body surface or lines a body cavity Two main types (by location): 1. Covering and lining epithelia On external and internal surfaces 2. Glandular epithelia Secretory tissue in glands

4 Characteristics of Epithelial Tissue 1. Cells have polarity apical (upper, free) and basal (lower, attached) surfaces Apical surfaces may bear microvilli (e.g., brush border of intestinal lining) or cilia (e.g., lining of trachea) Noncellular basal lamina of glycoprotein and collagen lies adjacent to basal surface

5 Characteristics of Epithelial Tissue 2. Are composed of closely packed cells Continuous sheets held together by tight junctions and desmosomes 3. Supported by a connective tissue reticular lamina (under the basal lamina) 4. Avascular but innervated 5. High rate of regeneration

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7 Characteristics of Epithelial Tissue 2. Are composed of closely packed cells Continuous sheets held together by tight junctions and desmosomes 3. Supported by a connective tissue reticular lamina (under the basal lamina) 4. Avascular but innervated 5. High rate of regeneration

8 Classification of Epithelia Ask two questions: 1. How many layers? 1 = simple epithelium >1 = stratified epithelium 2. What type of cell? Squamous Cuboidal Columnar (If stratified, name according to apical layer of cells)

9 Classification of Epithelia

10 Overview of Epithelial Tissues For each of the following types of epithelia, note: Description Function Location

11 Simple Epithelia One layer thick Primary functions: Absorption Secretion Filtration

12 (a) Simple squamous epithelium Description: Single layer of flattened cells with disc-shaped central nuclei and sparse cytoplasm; the simplest of the epithelia. Function: Allows passage of materials by diffusion and filtration in sites where protection is not important; secretes lubricating substances in serosae. Location: Kidney glomeruli; air sacs of lungs; lining of heart, blood vessels, and lymphatic vessels; lining of ventral body cavity (serosae). Air sacs of lung tissue Nuclei of squamous epithelial cells Photomicrograph: Simple squamous epithelium forming part of the alveolar (air sac) walls (125x). Figure 4.3a

13 Epithelia: Simple Squamous Two other locations Endothelium The lining of lymphatic vessels, blood vessels, and heart Mesothelium The epithelium of serous membranes in the ventral body cavity

14 (b) Simple cuboidal epithelium Description: Single layer of cubelike cells with large, spherical central nuclei. Function: Secretion and absorption. Location: Kidney tubules; ducts and secretory portions of small glands; ovary surface. Simple cuboidal epithelial cells Basement membrane Connective tissue Photomicrograph: Simple cuboidal epithelium in kidney tubules (430x). Figure 4.3b

15 (c) Simple columnar epithelium Description: Single layer of tall cells with round to oval nuclei; some cells bear cilia; layer may contain mucussecreting unicellular glands (goblet cells). Function: Absorption; secretion of mucus, enzymes, and other substances; ciliated type propels mucus (or reproductive cells) by ciliary action. Location: Nonciliated type lines most of the digestive tract (stomach to anal canal), gallbladder, and excretory ducts of some glands; ciliated variety lines small bronchi, uterine tubes, and some regions of the uterus. Simple columnar epithelial cell Basement membrane Photomicrograph: Simple columnar epithelium of the stomach mucosa (860X). Figure 4.3c

16 (d) Pseudostratified columnar epithelium Description: Single layer of cells of differing heights, some not reaching the free surface; nuclei seen at different levels; may contain mucussecreting cells and bear cilia. Cilia Mucus of mucous cell Function: Secretion, particularly of mucus; propulsion of mucus by ciliary action. Location: Nonciliated type in male s sperm-carrying ducts and ducts of large glands; ciliated variety lines the trachea, most of the upper respiratory tract. Trachea Photomicrograph: Pseudostratified ciliated columnar epithelium lining the human trachea (570x). Pseudostratified epithelial layer Basement membrane Figure 4.3d

17 Stratified Epithelia Two or more cell layers Regenerate from below More durable Primary functions: Protection

18 (e) Stratified squamous epithelium Description: Thick membrane composed of several cell layers; basal cells are cuboidal or columnar and metabolically active; surface cells are flattened (squamous); in the keratinized type, the surface cells are full of keratin and dead; basal cells are active in mitosis and produce the cells of the more superficial layers. Stratified squamous epithelium Function: Protects underlying tissues in areas subjected to abrasion. Location: Nonkeratinized type forms the moist linings of the esophagus, mouth, and vagina; keratinized variety forms the epidermis of the skin, a dry membrane. Photomicrograph: Stratified squamous epithelium lining the esophagus (285x). Nuclei Basement membrane Connective tissue Figure 4.3e

19 Epithelia: Stratified Cuboidal Quite rare in body Found in some sweat and mammary glands Typically two cell layers thick

20 Epithelia: Stratified Columnar Limited distribution in body Small amounts in pharynx, male urethra, and lining some glandular ducts Also occurs at transition areas between two other types of epithelia

21 (f) Transitional epithelium Description: Resembles both stratified squamous and stratified cuboidal; basal cells cuboidal or columnar; surface cells dome shaped or squamouslike, depending on degree of organ stretch. Function: Stretches readily and permits distension of urinary organ by contained urine. Location: Lines the ureters, urinary bladder, and part of the urethra. Transitional epithelium Basement membrane Connective tissue Photomicrograph: Transitional epithelium lining the urinary bladder, relaxed state (360X); note the bulbous, or rounded, appearance of the cells at the surface; these cells flatten and become elongated when the bladder is filled with urine. Figure 4.3f

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23 Glandular Epithelia A gland is one or more cells that makes and secretes an aqueous fluid Classified by: Site of product release endocrine or exocrine Relative number of cells forming the gland unicellular (e.g., goblet cells) or multicellular

24 Endocrine Glands Ductless glands Secrete hormones that travel through lymph or blood to target organs Hormones regulatory chemicals secreted by exocytosis directly into the extracellular space

25 Exocrine Glands More numerous than endocrine glands Secrete products into ducts Secretions released onto body surfaces (skin) or into body cavities Examples include mucous, sweat, oil, and salivary glands

26 Unicellular Exocrine Glands Ductless secrete their products directly on the free surface of open body cavities most common are the goblet cells (mucus secreting cells) found in the epithelium of the trachea and the digestive tube.

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28 Multicellular Exocrine Glands Multicellular exocrine glands are composed of a duct and a secretory unit Classified according to: Duct type (simple or compound) Structure of their secretory units (tubular, alveolar, or tubuloalveolar)

29 Simple duct structure (duct does not branch) Compound duct structure (duct branches) Tubular secretory structure Simple tubular Example Intestinal glands Simple branched tubular Example Stomach (gastric) glands Compound tubular Example Duodenal glands of small intestine Alveolar secretory structure Simple alveolar Example No important example in humans Simple branched alveolar Example Sebaceous (oil) glands Compound alveolar Example Mammary glands Compound tubuloalveolar Example Salivary glands Surface epithelium Duct Secretory epithelium Figure 4.5

30 Modes of Secretion Merocrine Products are secreted by exocytosis (e.g., pancreas, sweat and salivary glands) Holocrine Products are secreted by rupture of gland cells (e.g., sebaceous glands)

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32 Which of the following best describes a tissue? A group of organs working together for a common purpose A group of cells that have a similar structure and function The collection of all organelles in a cell Organs such as the heart or liver

33 An area in the body exposed to the external environment would be composed of which of the following tissue types? Epithelial tissue Connective tissue Muscle tissue Nervous tissue

34 Which of the following tissue types would you expect to find on a surface of the body that is subjected to a friction? Epithelial tissue Connective tissue Muscle tissue Nervous tissue

35 Which characteristic of epithelial tissues would you expect to find in a duct that is subject to a high degree of pressure (such as the male urethra)? Cuboidal shape Simple layering Pseudostratified layering Stratified layering

36 Which of the following types of epithelial tissues is best suited for areas of the body where diffusion or filtration occurs? Stratified columnar Simple cuboidal Simple squamous Stratified squamous

37 Which of the following specialized terms reflects the epithelial tissue found lining the inside of blood and lymph vessels? Epithelium Endothelium Mesothelium Squathelium

38 The presence of which type of epithelial tissue is a dead giveaway for glands? Simple squamous Stratified squamous Transitional epithelium Simple cuboidal

39 The mucus-secreting cells prevalent in simple columnar epithelium are known as. goblet cells cup cells chalice cells mucocells

40 The major distinction between endocrine glands and exocrine glands is that endocrine glands secrete their product into. the blood a duct the stomach the bladder